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Graph of oscillating mass

  1. Aug 11, 2006 #1
    Hello

    Just wondering when there is a graph of distance vs time for an oscillating mass in SHM and the graph is a sine curve and it asks us for the period-do we just find the time it takes for one wave to be completed? say the x-axis is eg: 1 2 3 4 5 6 etc etc and the wave is completed between 5 and 6 (closer to 5) do we just estimate the period from there say 5.2 seconds or is there another way?

    Also how do we find the speed is it just v=d/t where d=amplitude and t=time period?

    Thanks
    physics_06er
     
  2. jcsd
  3. Aug 11, 2006 #2

    Päällikkö

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    Homework Helper

    Yes, one period is the time taken to complete one whole oscillation.

    By definition: v = dx / dt, where x is the displacement of the mass, so you'll have to differentiate. Alternatively you could use the conservation of energy principle.
     
    Last edited: Aug 11, 2006
  4. Aug 11, 2006 #3
    Hi there

    Thanks for the reply..yeah i get that the period is defined by the time it takes for one wave to be completed but how do i get the time (period) from the graph if it isn't exactly on a point on the x-axis. do i just estimate eg: like what i said in my first post?

    Thanks
    physics_06er
     
  5. Aug 11, 2006 #4

    jtbell

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    Staff: Mentor

    If the tick marks are close together, then just estimate the nearest tenth of a space by eye. With some practice you can get it to within plus or minus a tenth of a space pretty easily.

    If the tick marks are far enough apart that you can measure the distance with a ruler, then measure the tick spacing, and the distance of the point you want from the lower tick, and calculate a proportion.
     
  6. Aug 12, 2006 #5
    thanks...but you know for the max. speed i know Päällikkö said"By definition: v = dx / dt, where x is the displacement of the mass, so you'll have to differentiate. Alternatively you could use the conservation of energy principle." but still im a bit unsure on what you mean. does anyone know of a good site that i can refer to? if i do amplitude/period will i get it wrong?

    thanks
    physics_06er
     
  7. Aug 12, 2006 #6

    jtbell

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    Staff: Mentor

    You didn't say before that you specifically needed to find the maximum speed. Maybe the following questions will jog you in the right direction:

    1. At what point(s) in the cycle does the mass have maximum speed?

    2. What does the speed (velocity) of an object correspond to, on a graph of the object's position versus time? Or: if you're supposed to be able to use calculus, you should know that the velocity is the derivative of the position: v = dx/dt. What do derivatives in general correspond to, in terms of graphs?
     
  8. Aug 12, 2006 #7

    Päällikkö

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    I suspected the methods calculus might be out of the scope of the course you're on, that's why I gave a subtle hint in the direction of energy conservation. See jtbell's post for further help.

    If you are genuinely interested in learning physics, see:
    http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/index.htm
    Those are physics video lectures from MIT. Great stuff, but does require some prior knowledge on vectors and calculus (depending on the grade you're on, you might already be familiar with these).

    Yes.
     
  9. Aug 12, 2006 #8
    Hi

    Thanks for the replies...yeah I did calc. up to last yr of High school (last year) but the course I'm doing at the moment is a music/physics paper which we have have to know the basics of phsyics and music (if that makes sense) so it's not like real hard physics...anyway thanks for the help...the link you gave looks good..

    Thanks again
    physics_06er
     
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